This invention relates to systems for optically inspecting cylindrical surfaces such as the cylindrical surfaces of cigarettes.
It is highly desirable to be able to inspect the entire cylindrical surface of cylindrical objects such as cigarettes. Any of a wide variety of defects may occur in such objects, and it is desirable to have automated equipment for detecting those defects so that defective objects can be rejected and/or so that any malfunctioning of the machinery producing those objects can be promptly identified and corrected. In the case of cigarettes, for example, the cylindrical surface may be defective due to a piece of tobacco stem piercing the paper, an imperfection in the way the filter has been joined to the remainder of the cigarette (including the possible complete absence of the intended filter), an imperfectly formed side seal which leaves some of the tobacco visible, a discoloration of the paper, etc.
Although inspection of this kind may take place at any stage in the production of the cigarettes, it can be advantageous to perform such inspection after processing of the individual cigarettes is complete or substantially complete. At this point in their fabrication, the individual cigarettes are most easily moved through the cigarette making machinery transverse to their length. This makes it difficult to use known cylindrical surface inspection apparatus such as that shown, for example, in Heitmann et al. U.S. Pat. No. 4,645,921, which requires the cigarettes to be passed longitudinally through the inspection apparatus.
On the other hand, with the cigarettes moving transverse to their length it is much more difficult to image the entire surface of the cigarette. For example, the cylindrical nature of the surface makes uniform illumination of the surface and elimination of shadows difficult. Thus, it may be necessary to inspect the surface piecemeal, but it is highly desirable to keep the number of inspections to a minimum in order to avoid undue proliferation of the inspection components.
It should also be noted that any successful inspection system for products such as cigarettes must be extremely fast in order to keep pace with the high speeds at which such products are typically made. For example, it is now common for a single cigarette making machine to make cigarettes at rates approaching 10,000 per minute. A successful cigarette inspection system must also be able to inspect for relatively small and/or subtle defects (e.g., a hole as small as about 0.5 millimeter in diameter or a minor discoloration of the cigarette paper).
In view of the foregoing, it is an object of this invention to improve and simplify systems for inspecting cylindrical surfaces.
It is a more particular object of this invention to provide cylindrical surface inspection systems which are capable of inspecting the entire circumference of such surfaces at very high speeds.